The present invention relates to a tape threading arrangement for a VTR (video tape recorder), and more particularly to one that threads tape from a cassette around a drum with substantially a 360 degree wrap angle.
In helical scan video recording, a magnetic tape is drawn from a supply reel, wrapped around a drum having a magnetic recording head disposed therein, and then provided to a supply reel. A 360 degree wrap angle allows the drum diameter to be one-half the size of a 180 degree wrap angle configuration for compactness. If the one-half diameter 360 degree drum is rotated at twice the angular speed of the 180 degree drum the same head-to-tape speed is achieved as well as a one field per revolution, non-segmented picture. To achieve further compactness, and also convenience of loading and removal, it is desirable to have the supply and take-up reels coaxially mounted one above the other in a cassette. However, it is difficult to provide automatic threading of tape from a cassette with a 360 degree wrap angle around a drum.
One solution is shown in U. S. Pat. No. 4,191,979. As shown therein, a pair of kidney-shaped "grippers" are used to achieve the threading. However, the grippers are relatively long, and therefore when in their initial position, which is longitudinally disposed between the reels and the drum, a relatively large space must be provided for them. This is done by having a relatively large space between the reels and the drum. For certain applications, such as a VTR used with an ENG (electronic news gathering) camera, this space may be too large.
It is therefore desirable to provide a compact threading arrangement for a 360 degree wrap angle of tape from a cassette.